Overmolded electronic module with an integrated electromagnetic shield using SMT shield wall components

ABSTRACT

An electronic module with an integrated electromagnetic shield using surface mount shield wall components has been disclosed. Each surface mount shield wall component provides side shielding of circuitry within the overmolded electronic module and provides an exposed conductive shield wall section to which a top conductive shield can be applied. By including the shield structure as part of the overmolded electronic module, the need for a separate shield and separate process steps for installing the separate shield can be eliminated. Each surface mount shield wall component comprises a non-conductive portion that provides stability during a reflow soldering process, but at least a sacrificial portion of the non-conductive portion can be removed to reduce the amount of area occupied by the overmoldable shield structure.

This application is a continuation in part of, and claims benefit of thefiling date of, and hereby incorporates fully by reference, the pendingparent application entitled “Overmolded Semiconductor Package with anIntegrated EMI and RFI Shield” Ser. No. 10/793,618, filed Mar. 4, 2004,and assigned to the assignee of the present application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to electronic device manufacturing andmore particularly to techniques for providing shielding for electroniccomponents.

2. Related Art

Portable electronic devices such as cell phones typically utilizeelectronic modules to provide a high level of functionality in a smallpackage. The electronic module can include, for example, any combinationof one or more integrated circuits and one or more passive devices suchas resistors, capacitors, and inductors mounted on a module circuitboard. The components of the electronic module can be encapsulated usinga non-conductive material to form an overmolded electronic modulepackage. Electronic circuits within an electronic module typicallyreceive, transmit, and/or internally utilize time-varyingelectromagnetic signals. Such electromagnetic signals can radiatethrough the non-conductive packaging material of the electronic moduleand affect other electronic devices (e.g., cause interference), exceedregulatory limits, and/or be subject to interception. Also, externallypresent electromagnetic energy of either natural or artificial originmay penetrate non-conductive packaging material of an electronic moduleto adversely affect the circuitry within the electronic module.Accordingly, good engineering practices dictate that electromagneticshielding be provided to attenuate electromagnetic energy to limitpotentially adverse effects. Typically electromagnetic shielding isprovided by surrounding the electronic module with a conductive materialsuch as a structure that is stamped or otherwise formed out of a thinsheet of metal. However, such a shield typically takes up substantialspace around the electronic module. Such a stamped shield needs to belarge enough to avoid mechanically interfering with the electronicmodule. Moreover, the dimensions of the shield have to be sufficient toaccommodate manufacturing tolerances of the electronic module, as wellas those of the shield. The additional size required by a stamped shieldlimits miniaturization of products including such electronic modules.Another disadvantage of a stamped shield is that attaching the shieldinvolves an additional manufacturing step that cannot be performed untilafter installing the electronic module.

Thus, a technique for providing electromagnetic shielding that avoidssuch disadvantages is needed.

SUMMARY OF THE INVENTION

The present invention is directed to a method and apparatus forproviding an overmolded electromagnetic shield for an electronic module.The invention addresses and resolves the need in the art for a costeffective shield for an overmolded electronic module that does notsubstantially increase the module size and overcomes the need for aseparate shield, such as a stamped shield, and a separate process forinstalling the separate shield.

According to one exemplary embodiment, an overmolded electronic moduleincludes any combination of one or more integrated circuits and passiveSMT (surface mount technology) components situated on a module circuitboard. The overmolded electronic module further includes one or more SMTshield wall components situated on the same module circuit board wherethe SMT shield wall components form the side walls of an electromagneticshield. The overmolded electronic module further includes an overmoldmaterial used to encapsulate the components within the electronicmodule. The overmolded electronic module further includes a conductivelayer situated on the top surface of the overmold material where theconductive layer forms the top of an electromagnetic shield. Accordingto this exemplary embodiment, the conductive layer that forms the top ofthe electromagnetic shield is electrically connected to the SMT shieldwall components which in turn are electrically connected to SMT pads onthe module circuit board in such a way that the components within theelectronic module are surrounded by the shielding structure.

In accordance with at least one embodiment, the SMT shield wallcomponents have form factors compatible with existing SMT componentassembly requirements. For example, the SMT shield wall components maybe implemented in a size and shape similar to a typical SMT component,such as a resistor or capacitor, but with a body of sacrificial,nonconductive material joining the conductive shield wall sections.Accordingly, the SMT shield wall components may be placed in anelectronic module using typical SMT component assembly processes, forexample typical SMT pick and place processes.

Multiple module circuit boards can be arranged in an array on a circuitboard panel or strip with a space between the module circuit boards thatis used as a saw street when the module circuit boards go through asingulation process. The design of the SMT shield wall components allowsthem to be placed between module circuit boards in the saw street suchthat one SMT shield wall component can provide a first shield wallsection for a given module circuit board and a second shield wallsection for an adjacent module circuit board. The result is a shieldwall component that has a footprint that is large enough relative to theheight of the shield wall component to be easy to manufacture and toprovide mechanical stability and withstand subsequent overmoldingprocesses while occupying minimal space in the final completedovermolded electronic module since much of the SMT shield wall component(e.g., a sacrificial portion) is situated in the saw street and isremoved during the singulation process.

Other features and advantages of the present invention will become morereadily apparent to those of ordinary skill in the art after reviewingthe following detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, 1C, and 1D are diagrams of a surface mount technology(SMT) shield wall component comprising two conductive wall sections thatare situated at the ends of a non-conductive, sacrificial portion inaccordance with at least one embodiment. FIG. 1A is a top view diagramof the SMT shield wall component. FIG. 1B is an end view diagram of theSMT shield wall component. FIG. 1C is a side view diagram of the SMTshield wall component. FIG. 1D is a perspective view diagram of the SMTshield wall component.

FIG. 2 is a plan view diagram of a circuit board panel for overmoldedelectronic modules with an integrated electromagnetic shield using SMTshield wall components that includes multiple module circuit boardsarranged in an array with saw streets situated between the individualmodule circuit boards in accordance with at least one embodiment.

FIG. 3A is a top view diagram of a module circuit board with exposedconductive portions of SMT shield wall components in accordance with atleast one embodiment.

FIG. 3B is a side view diagram of a module circuit board with exposedconductive portions of SMT shield wall components in accordance with atleast one embodiment.

FIG. 4A is a top view diagram of a module circuit board with a topconductive shield coupled to exposed conductive portions of SMT shieldwall sections in accordance with at least one embodiment.

FIG. 4B is a side view diagram of a module circuit board with a topconductive shield coupled to exposed conductive portions of SMT shieldwall sections in accordance with at least one embodiment.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a method and apparatus for anelectronic module with an overmolded electromagnetic shield using SMTshield wall components. The following description contains specificinformation pertaining to the implementation of the present invention.One skilled in the art will recognize that the present invention may beimplemented in a manner different from that specifically discussed inthe present application. Moreover, some of the specific details of theinvention are not discussed in order not to obscure the invention. Thespecific details not described in the present application are within theknowledge of a person of ordinary skill in the art.

The drawings in the present application and their accompanying detaileddescription merely describe exemplary embodiments of the invention. Tomaintain brevity, other embodiments of the invention which use theprinciples of the present invention are not specifically described inthe present application and are not specifically illustrated by thepresent drawings. It should be noted that similar numerals generallyrefer to similar elements in the various drawings.

The method and apparatus for providing an electromagnetic shieldstructure using an SMT shield wall component that can be at leastpartially integrated within an overmolded part, for example, anelectronic module within a module circuit board which includesintegrated circuits, and surface mount components. Surface mountedcomponents within the electronic module are typically attached to amodule circuit board residing in a circuit board panel using a pick andplace process. A reflow soldering process is used to solder the surfacemount components to the circuit board. To provide a top conductiveshield connection a conductive structure is needed that-extends abovethe height of the integrated circuits and/or surface mount components.However, tall conductive structures tend to lose mechanical stabilityand become misaligned during the reflow soldering process. If an attemptis made to increase the width of the tall conductive structure toincrease its stability, the additional width could reduce usable surfacearea of the circuit board which results in a significant increase in thesize of the circuit board and the complete electronic module.

According to at least one embodiment, a SMT shield wall component isprovided that is similar enough to form factors of existing componentsto allow compatibility with SMT pick and place processes, but whichprovides a sacrificial non-conductive portion that provides increasedstability during reflow soldering processes but can be subsequentlyremoved if the SMT shield wall component is mounted so that thesacrificial portion is located over the saw street. This reduces thesize of the SMT shield wall component to an optimal size for providing aside wall shielding structure and shielding structure interconnect to atop conductive shield structure. The SMT shield wall component comprisesa non-conductive sacrificial portion and a first conductive shield wallsection coupled to the non-conductive sacrificial portion. The surfacemount component typically comprises a second conductive shield wallsection coupled to the non-conductive sacrificial portion opposite thefirst conductive shield wall section.

Unlike traditional surface mount components, a SMT shield wall componentwould not need conductive internal portions. Rather, providing anon-conductive sacrificial portion coupled to a conductive shield wallsection would allow the non-conductive sacrificial portion to be removed(e.g., by sawing) without releasing conductive debris that might settleand form undesired electrical connections. Preferably, thenon-conductive sacrificial portion comprises epoxy or another polymerresin similar to the nonconductive overmold material used forovermolding the entire electronic module. One or more conductive shieldwall sections remain after removal of the non-conductive sacrificialportion of the SMT shield wall component to provide side wall shieldingand connection to a top conductive shield. The one or more conductiveshield wall sections preferably comprise metal (e.g., tin plated copper)that may be preferably soldered to the conductive circuit board padsupon which the SMT shield wall components may be mounted. The conductivecircuit board pads are preferably connected to a ground plane within thecircuit board. The conductive circuit board pads are optionallyconnected to package pins on the electronic module that are subsequentlyconnected to a ground plane within the module circuit board on which theelectronic module is mounted.

The presently available pick and place process for mounting surfacemount components can be used to mount surface mount shield wallcomponents as well as other passive and/or discrete surface mountcomponents, which are preferably mounted and reflow soldered beforemounting and wirebonding any integrated circuits that may be included inthe electronic module.

After being populated with components (e.g., integrated circuits and/orpassive SMT components), an environmentally protective material (e.g., amold compound) may be applied to the circuit board panel (e.g., byinjection molding) to cover the one or more electronic modules residingon the circuit board panel. After the overmold process is complete, theconductive shield wall sections of the SMT shield wall components areexposed (e.g. by milling or planing the top surface of the overmoldedcircuit board panel) in order to provide an electrical connection to thetop conductive shield. Thereafter, a conductive material is applied tothe top surface of the module circuit boards to form the top conductiveshield. After the conductive material is applied to form the topconductive shield, the circuit board panel is singulated into individualelectronic modules, each residing in a respective module circuit board.During singulation, a saw cuts through a saw street, which is asacrificial margin between module circuit boards defined on a circuitboard panel. The singulation saw, while removing the circuit boardmaterial and mold compound along the saw street, also removes thenon-conductive sacrificial portion of the SMT shield wall component.

Surface mount shield wall components may be mounted around a peripheryof an electronic module circuit board. Alternatively or in conjunctionwith ones mounted around the periphery, surface mount shield wallcomponents may be mounted internal to an electronic module circuitboard, for example to provide intramodule shielding.

The SMT shield wall components in accordance with at least oneembodiment described herein are useful for electronic modules thattransmit, receive, or internally utilize electromagnetic energy, forexample, signals in the 100 MHz to 5 GHz range. An example of a modulecircuit board for which the SMT shield wall components would be usefulis a radio-frequency (RF) module, for example, a power amplifier module(PAM), a transmit front-end module (TXFEM), a voltage-controlledoscillator (VCO), a RF mixer, etc.

FIGS. 1A, 1B, 1C, and 1D show different views of a surface mounttechnology (SMT) shield wall component comprising a non-conductivesacrificial portion in accordance with at least one embodiment. FIG. 1Ais a top view diagram of the SMT shield wall component. The SMT shieldwall component comprises conductive shield wall section 102 and,optionally, conductive shield wall section 103, as well asnon-conductive portion 101, including non-conductive sacrificial portion104. Non-conductive portion 101 is coupled to conductive shield wallsections 102 and, if present, shield wall section 103. Sacrificialportion 104 of the SMT shield wall component need not be of precisewidth, but may vary in width, for example, depending on processparameters, such as singulation saw kerf width. For some uses (e.g.,intramodule shielding), sacrificial portion 104 need not be removed, butmay be left intact.

FIG. 1B is an end view diagram of the SMT shield wall component. Whilethe SMT shield wall component comprises non-conductive portion 101,including non-conductive sacrificial portion 104, only shield wallsection 102 is depicted in this end view diagram. FIG. 1C is a side viewdiagram of the SMT shield wall component. Conductive shield wall section102, non-conductive portion 101, and optional conductive shield wallsection 103 are depicted in FIG. 1C. FIG. 1D is a perspective viewdiagram of the SMT shield wall component. Shield wall section 102,non-conductive portion 101, and optional shield wall section 103 aredepicted in FIG. 1D.

FIG. 2 is a plan view diagram of circuit board panel 201 in accordancewith at least one embodiment. Circuit board panel 201 comprises modulecircuit boards 202, 203, 204, and 205. Conductive pads are provided onmodule circuit boards 202, 203, 204, and 205, either around theperiphery of the module circuit boards and/or internal to the modulecircuit boards, to allow mounting of SMT shield wall components. FIG. 2depicts SMT shield wall components mounted on such pads, for example,SMT shield wall components 206 through 241 are mounted around theperiphery of module circuit boards 202 through 205 and SMT shield wallcomponents 248 and 249 mounted internal to module circuit board 203.

As illustrated, by using SMT shield wall components having a firstconductive shield wall section on one end coupled to a non-conductivesacrificial portion in the middle, which is in turn coupled to a secondconductive shield wall section on the opposite end, the first conductiveshield wall section (e.g., the first conductive shield wall section ofSMT shield wall component 214) can be mounted on a pad at the peripheryof a first module circuit board (e.g., module circuit board 202), whilethe second conductive shield wall section (e.g., the second conductiveshield wall section of SMT shield wall component 214) can be mounted ona pad at the periphery of a module second circuit board (e.g., modulecircuit board 204). Such bridging of adjacent module circuit boards by aSMT shield wall component allows the first conductive shield wallsection of the SMT shield wall component to be used to provide side wallshielding and coupling to a top conductive shield for the module firstcircuit board while using the second conductive shield wall section ofthe SMT shield wall component to be used to provide side wall shieldingand coupling to a top conductive shield for the second module circuitboard. The non-conductive sacrificial portion of the SMT shield wallcomponent between the first and second conductive shield wall sectionsof the SMT shield wall component can be removed along with circuit boardmaterial between the module first circuit board and the second modulecircuit board by singulating the module circuit boards, for example,using a singulation saw. Singulation can occur along paths through thecircuit board and/or SMT shield wall components, for example, cuttingpaths 242, 243, 244, 245, 246, and/or 247 depicted in FIG. 2.

FIG. 3A is a top view diagram of electronic module 301 with exposedconductive shield wall sections of the SMT shield wall components inaccordance with at least one embodiment. The top portions of conductiveshield wall sections of the SMT shield wall components may be exposedeither by using an overmolding process that allows them to remainexposed or by using a material removal process after overmolding toexpose the conductive shield wall sections of the SMT shield wallcomponents. Examples of such material removal processes include milling,grinding, lasing, and/or planing. With the conductive shield wallsections 306, 307, 308, 309, 310, 311, 312, 313, 314, 315, 316, and 317of the SMT shield wall components exposed, the remaining components onmodule circuit board 318 preferably remain encapsulated within the moldcompound, as depicted in side view FIG. 3B.

FIG. 3B is a side view diagram of electronic module 301 with exposedconductive portions of the SMT shield wall components in accordance withat least one embodiment. In accordance with at least one embodiment, thetops of conductive shield wall sections, such as exemplary shield wallsections 310, 311, 312, and 313 are flush with the top of theencapsulant, i.e. mold compound 330 of electronic module 301. The topsof other surface mount components, such as exemplary SMT components 319,320, and 321 are below the tops of the conductive shield wall sections,such as exemplary shield wall sections 310, 311, 312, and 313, and arepreferably covered with encapsulant, i.e., mold compound 330.

FIGS. 4A and 4B are top and side view diagrams of electronic module 301with top conductive shield 401 coupled to exposed conductive shield wallsections of the SMT shield wall components in accordance with at leastone embodiment. With the conductive shield wall sections 306 through 317of the SMT shield wall components exposed, top conductive shield 401 canbe applied over the exposed conductive shield wall sections 306 through317 of the SMT shield wall components and preferably over the moldcompound that remains. For example, top conductive shield 401 may be aconformal coating, such as a conductive paint or conductive epoxy, or athin layer of metal, which may attached (e.g. soldered) to the exposedconductive shield wall sections 306 through 317 of the SMT shield wallcomponents.

Thus, as described above and according to the present invention,multiple module circuit boards can be arranged in an array on a circuitboard panel or strip with a space between the module circuit boards thatis used as a saw street when the module circuit boards go through asingulation process. Prior to the singulation process, the SMT shieldwall components may be placed in the saw streets between module circuitboards using typical SMT component assembly processes, for exampletypical SMT pick and place processes. The design of the SMT shield wallcomponents allows them to be placed between module circuit boards in thesaw street such that one SMT shield wall component can provide a firstshield wall section for a given module circuit board and a second shieldwall section for an adjacent module circuit board. The result is ashield wall component that has a footprint that is large enough relativeto the height of the shield wall component to be easy to manufacture andto provide mechanical stability and withstand subsequent overmoldingprocesses while occupying minimal space in the final completedovermolded electronic module since much of the SMT shield wall component(e.g., a sacrificial portion) is situated in the saw street and isremoved during the singulation process.

From the above description of the invention it is manifest that varioustechniques can be used for implementing the concepts of the presentinvention without departing from its scope. Moreover, while theinvention has been described with specific reference to certainembodiments, a person of ordinary skill in the art would appreciate thatchanges can be made in form and detail without departing from the spiritand the scope of the invention. Thus, the described embodiments are tobe considered in all respects as illustrative and not restrictive. Itshould also be understood that the invention is not limited to theparticular embodiments described herein but is capable of manyrearrangements, modifications, and substitutions without departing fromthe scope of the invention.

Thus, a method and apparatus for an overmolded electronic module with anintegrated electromagnetic shield using SMT shield wall components hasbeen described.

1. A surface mount shield wall component for providing side wallshielding for an electronic module and suitable for connection to a topconductive shield of said electronic module, said surface mount shieldwall component comprising: at least one conductive shield wall sectionsuitable for attachment to a conductive circuit board pad of saidelectronic module; a non-conductive portion, including a non-conductivesacrificial portion, attached to said at least one conductive shieldwall section; wherein said conductive shield wall section provides saidside wall shielding and is suitable for connection to said topconductive shield.
 2. The surface mount shield wall component of claim 1wherein said surface mount shield wall component is positioned on acircuit board panel by an SMT pick and place process.
 3. The surfacemount shield wall component of claim 1 wherein said non-conductiveportions provides mechanical stability for said surface mount shieldwall component during an overmolding process.
 4. The surface mountshield wall component of claim 1 wherein said non-conductive portionlies in a saw street between two adjacent module circuit boards on acircuit board panel, so as to facilitate removal of said sacrificialportion by sawing.
 5. The surface mount shield wall component of claim 1wherein said electronic module is substantially overmolded with a moldcompound so as to form an overmolded electronic module.
 6. The surfacemount shield wall component of claim 5 wherein said mold compound isremoved from a top portion of said at least one conductive shield wallsection so as to expose said top portion for connection to said topconductive shield.
 7. The surface mount shield wall component of claim 6wherein said top conductive shield is placed on said overmoldedelectronic module for connection to said at least one conductive shieldwall section.
 8. The surface mount shield wall component of claim 1wherein said conductive circuit board pad is coupled to a ground planeof a module circuit board supporting said electronic module.
 9. Thesurface mount shield wall component of claim 1 wherein said conductivecircuit board pad is coupled to a package pin of said electronic module,said package pin being coupled to a ground plane of a module circuitboard supporting said electronic module.
 10. An overmolded electronicmodule comprising: a plurality of SMT shield wall components arranged onperiphery of a module circuit board; at least one integrated circuitsituated in said module circuit board; a top conductive shield connectedto an exposed top portion of at least one of said plurality of SMTshield wall components.
 11. The overmolded electronic module of claim 10further including at least one passive SMT component situated in saidmodule circuit board.
 12. The overmolded electronic module of claim 10wherein said top conductive shield is situated on a mold compoundencapsulating said electronic module, and wherein said exposed topportion is not covered by said mold compound.
 13. The overmoldedelectronic module of claim 10 wherein said at least one of saidplurality of SMT shield wall components includes a conductive shieldwall section.
 14. The overmolded electronic module of claim 13 whereinan exposed top portion of said conductive shield wall section isconnected to said top conductive shield.
 15. The overmolded electronicmodule of claim 13 wherein said conductive shield wall section isattached to a conductive circuit board pad of said module circuit board.16. The overmolded electronic module of claim 15 wherein said conductivecircuit board pad is coupled to a ground plane of said module circuitboard.
 17. The overmolded electronic module of claim 13 wherein saidconductive shield wall section comprises tin plated copper.
 18. Theovermolded electronic module of claim 10 wherein at least one additionalSMT shield wall component is situated inside said module circuit board.19. The overmolded electronic module of claim 10 wherein said moldcompound comprises a polymer resin.